Transendocardial Cell Delivery In Post‑Acute Myocardial Infarction

By Ibon Garitaonandia, Ph.D., chief scientific officer, CellProthera

Myocardial infarction (MI) remains a leading cause of heart failure worldwide despite major advances in reperfusion and pharmacologic therapy. Even with timely primary percutaneous coronary intervention (PCI), substantial microvascular damage persists in many patients, leading to impaired myocardial perfusion, scar expansion, and adverse ventricular remodeling during the post‑acute period.¹  

These changes set in motion a cascade of adverse remodeling, which unfolds primarily during the post‑acute phase (one to four weeks after the infarction). For this reason, the post‑acute period has become an increasingly attractive therapeutic window for cell‑based regenerative strategies aiming to preserve myocardium, enhance microvascular perfusion, support ventricular recovery, and attenuate remodeling.

Among the various cell types under clinical evaluation, CD34+ cells have shown the strongest biological rationale for promoting neovascularization, tissue perfusion, and cytoprotection.^2,3 Our team has developed ProtheraCytes, an autologous CD34+‑enriched cell therapy produced via a proprietary ex vivo expansion process. Developing such therapies has highlighted a crucial determinant of therapeutic success: the route of administration.

In cardiac cell therapy, how cells are delivered may be just as important as what cells are delivered. Among the available approaches — intracoronary infusion, intravenous injection, and transendocardial administration — the latter has emerged as a particularly effective technique for targeting cells into ischemic border zones at risk during the post‑AMI period.

This article provides an in‑depth analysis of why transendocardial delivery offers significant advantages in the context of post‑AMI cell therapy and details the advantages of specialized delivery systems such as the C‑Cath catheter, designed to optimize retention, distribution, and safety.

The Post‑Acute Window: A Therapeutic Opportunity For Regeneration

The post‑acute period following ST-segment elevation myocardial infarction (STEMI) is characterized by reorganization of inflammatory infiltrates, initiation of collagen deposition, transition from inflammatory to reparative phases, high susceptibility to infarct expansion, and ongoing microvascular dysfunction.⁴ Core regions of necrosis are surrounded by a heterogeneous border zone characterized by partial ischemia, inflammation, impaired microvascular perfusion, and vulnerability to remodeling. This is a phase when the myocardium remains partially salvageable, and interventions that enhance perfusion or stabilize the border zone may substantially influence long‑term ventricular function.

The Rationale For Localized Delivery In Post‑Acute Myocardial Infarction

The border zone is the primary target for regenerative strategies. However, systemic or intracoronary delivery methods face substantial biological barriers:

• Impaired coronary microcirculation reduces the likelihood that infused cells will reach the target tissue.
• Endothelial dysfunction and capillary obstruction limit homing.
• Shear forces during intracoronary delivery decrease cell viability.
• Rapid washout from systemic circulation leads to poor myocardial retention (<5% in most studies).

These limitations underscore the need for direct intramyocardial administration, where cells can be deposited precisely within affected regions while avoiding systemic dispersion.

Why Transendocardial Injection? Mechanistic And Clinical Advantages

Transendocardial injection involves the placement of a specialized catheter system into the left ventricle via a retrograde transaortic approach. Guided by mapping technologies, operators can identify viable but ischemic myocardium and inject cells directly into targeted regions.

1. Superior Cell Retention

A core advantage is the markedly higher proportion of administered cells that remain in the myocardium. Studies comparing delivery routes consistently demonstrate:

• Transendocardial: 10%–20% retention^5,6,7
• Intracoronary: 2%–5% retention
• Intravenous: <1% retention

In regenerative medicine, where cell number and distribution are closely linked to therapeutic impact, this increased retention is critical.

2. Precise Anatomical Targeting

Mapping systems allow injection into areas of:

• reduced voltage (ischemic but viable myocardium)
• impaired perfusion
• high risk of expansion or akinesis.

This precision is not achievable with intracoronary or systemic approaches.

3. Enhanced Microvascular Neovascularization

By depositing pro‑angiogenic cells into ischemic border zones, transendocardial administration promotes:

• capillary density increase
• collateral vessel formation
• improved perfusion of hibernating myocardium.

These effects have been observed in studies of CD34+ cells^2,8 and other stem cell populations.

4. Reduced Washout And Immune Clearance

Localized injection avoids exposure to pulmonary first‑pass clearance (a major issue for intravenous delivery) and reduces exposure to high shear stress or turbulent flow, both of which impair viability.

5. Improved Clinical Outcomes In Cell Therapy Trials

Multiple early‑ and mid‑stage clinical trials using transendocardial delivery (e.g., ACT34‑CMI, TRIDENT, POSEIDON, EXCELLENT) have demonstrated:

• reduced angina burden
• improved left ventricular ejection fraction (LVEF)
• smaller infarct size
• improved perfusion and exercise tolerance.

The majority of functional improvements in cell therapy trials are associated with transendocardial — not intracoronary — delivery.

6. Delivery During The Post‑Acute Window

The post‑acute phase (days five to 30 after MI) represents an ideal period for intervention: inflammation is stabilizing, reperfusion injury has peaked, and the myocardium is entering the remodeling cascade. Transendocardial delivery is well suited to this window due to:

• procedural safety after acute stabilization
• capacity to target areas of remodeling visible on mapping
• reduced microvascular obstruction compared to the acute phase.

Comparison With Other Delivery Routes

1. Intracoronary Delivery

Although technically simple and widely used, intracoronary infusion suffers from significant limitations:

• dependent on microvascular integrity, often impaired after AMI
• cell loss due to washout and non‑specific distribution
• limited penetration into the myocardium
• potential for microvascular obstruction in high cell concentrations.

For these reasons, intracoronary routes have shown modest or inconsistent results in post‑AMI trials.

2. Intravenous Delivery

While noninvasive, it is generally considered ineffective for targeting the heart due to:

• most cells are trapped in the lungs
• minimal homing to ischemic myocardium
• low viability due to systemic immune clearance.

This route is typically excluded from serious cardiovascular regenerative programs.

3. Epicardial Injection

Epicardial injection can provide targeted delivery but requires thoracotomy or minimally invasive surgical access, making it unsuitable for post‑AMI patients who have recently undergone PCI and are on dual antiplatelet therapy.

Transendocardial Delivery Systems: The Importance Of Specialized Catheter Systems

Performing safe, consistent, and efficacious transendocardial injections relies heavily on catheter design. Key technical requirements include:

• precise navigation within the LV cavity
• stable tip anchoring
• controlled needle penetration
• minimal risk of perforation
• compatibility with 3D mapping systems
• ability to meter small volumes (100 to 300 μL) accurately.

The catheter needs to optimize delivery efficiency, safety, and reproducibility in transendocardial injection procedures. It should contain the following characteristics to be used in regenerative cardiology:

1. Optimized Needle Design For Controlled Penetration

The catheter should feature:

• a retractable, beveled, fine‑gauge needle
• preset penetration depth
• controlled tactile feedback.

This minimizes risks of over‑penetration and perforation — critical for post‑AMI myocardium, which may be thinned or friable.

2. High Precision Injection Control

The catheter should deliver small volumes at multiple injection sites, ensuring:

• homogeneous distribution
• minimized leakage
• optimal exposure of ischemic tissue to therapeutic cells.

3. Stability And Navigation

The catheter’s shaft and tip should be engineered to provide:

• excellent stability during contact
• consistent perpendicular orientation for injections
• improved control in complex cardiac anatomies.

This results in more reproducible injection depth and placement.

4. Compatibility With Mapping Systems

The catheter should be integrated with electro‑anatomical mapping systems, allowing:

• real‑time localization of viable but ischemic myocardium
• delivery into pre‑identified target zones
• efficient avoidance of scarred or akinetic regions.

Compatibility enhances accuracy and may improve therapeutic outcomes.

5. Reduced Cell Damage And Improved Viability

The catheter should have low‑shear, cell‑friendly lumen design to reduce mechanical stress on fragile cell populations, supporting:

• higher post‑delivery viability
• improved retention
• better functional performance.

This is a major technical distinction, as many standard catheters are optimized for drug injection rather than cell delivery.

6. Enhanced Operator Ergonomics And Procedure Efficiency

The system should facilitate multiple injections in a single procedure with:

• ergonomic plunger and control mechanisms
• simplified rotation and repositioning
• intuitive depth control.

These practical elements reduce operator fatigue and procedure time, which are important in routine clinical integration.

Safety Considerations

Transendocardial injection is generally safe when performed with dedicated catheters. Transendocardial injection is associated with:

• low incidence of perforation
• rare occurrence of pericardial effusion
• stable hemodynamic profiles during injection.

Implications For Future Regenerative Therapies

As cell therapies, such as our autologous CD34+ cell products, advance toward commercialization, the delivery route will be a critical differentiator for clinical efficacy and operational feasibility. Transendocardial administration:

• aligns with interventional cardiology workflows
• fits into post‑acute care pathways
• can be standardized for multicenter trials
• supports high‑value cell therapy products that depend on local therapeutic activity.

Advances in catheter engineering, imaging, and mapping will continue to augment the precision and therapeutic impact of transendocardial injections.

Conclusion

Transendocardial injection offers clear advantages over intracoronary, intravenous, and epicardial routes for delivering regenerative cell therapies in post‑acute myocardial infarction. Its superior retention, precise targeting, improved viability, and strong safety profile make it the preferred method for administering pro‑angiogenic cell therapies. Catheter systems designed specifically for myocardial cell delivery, such as the C-Cath catheter, further enhance these benefits through improved stability, injection control, mapping compatibility, and protection of cell integrity.

As the field of cardiovascular regenerative medicine advances toward commercial translation, optimized delivery technologies will play a critical role alongside cell biology, together shaping the next generation of therapies aimed at preventing heart failure after myocardial infarction.

References

1. Ibáñez B, et al. Eur Heart J. 2015;36:959–1004.
2. Asahara T, et al. Science. 1997;275:964–967.
3. Losordo DW, Dimmeler S. Circulation. 2004;109(22):2692-2697.
4. Menasché P. Nat Rev Cardiol. 2018;15:659–672.
5. Perin EC, et al. Circulation. 2003;107:2294–2302.
6. Vulliet PR, et al. Circulation. 2004;109:963–968.
7. Vrtovec B, et al. Circulation. 2013;128:S42-9.
8. Losordo DW, et al. Circulation. 2007;115:3165–3172.

About The Author

Ibon Garitaonandia, Ph.D., MBA, is the chief scientific officer at CellProthera, a French clinical‑stage biotechnology company developing stem cell–based therapies for post‑acute myocardial infarction and ischemic stroke. He brings extensive experience in advancing regenerative medicine programs from early discovery through clinical translation. Before joining CellProthera, Dr. Garitaonandia held executive and scientific leadership roles at the Richmond Research Institute, Histocell, and the International Stem Cell Corporation, where he led the development of stem cell–derived therapeutic candidates for multiple indications, including Parkinson’s disease and traumatic brain injury. He previously received a prestigious CIRM Postdoctoral Fellowship at the Center for Regenerative Medicine at The Scripps Research Institute. Dr. Garitaonandia holds a Ph.D. in Biochemistry from the University of Florida and a Bachelor’s degree in Chemistry from the University of the Basque Country.